Phase equilibria in Cu-Al-Zr system at 1073 K and aluminum concentration of less than 55 at %

X-ray diffraction and electron probe microanalysis were used to investigate phase equilibria in the ternary Cu-Al-Zr system at 1073 K in the Zr-rich region. The fragment of the isothermal section of the system was plotted. The regions of homogeneity of the ternary ZrCu₂Al and ZrCu _x Al_{2 ? x} phases were investigated. The type of phase equilibria between binary and ternary compounds of the Al-Cu-Zr system was established. It was found out that, at a Zr concentration above 55 at %, ternary compounds are not formed, and the Zr₃Al and Zr₂Cu phases were in equilibria with ??-Zr at 1073 K.     

The HfNi and ZrNi systems in the region 65 – 80 at.% Ni

The HfNi and ZrNi systems have been examined in the region 65 – 80 at.% Ni by microscope and X-ray analyses.In the HfNi system the following intermediate phases were observed: Hf₃Ni₇, Hf₈Ni₂₁, HfNi₃(h. t.), HfNi₃(l. t.) and Hf₂Ni₇. Hf₃Ni₇, which is formed peritectically at 1250 ± 20 °C, decomposes eutectoidally at 1016 ± 3 °C into Hf₇Ni₁₀ and HfNi₃(l. t.). Hf₈Ni₂₁ is stable from 1300 ± 20 °C, where it forms peritectically, to 1175 ± 10 °C where it decomposes eutectoidally into Hf₃Ni₇ and HfNi₃(l. t.). HfNi₃(h. t.) is a high temperature phase, forming peritectically at 1350 ± 20 °C and transforming into HfNi₃(l. t.) below 1200 ± 10 °C. Hf₂Ni₇ melts congruently. A eutectic between Hf₇Ni₁₀and Hf₃Ni₇ occurs at 1190 ± 10 °C.In the ZrNi system only one phase forming peritectically exists; this is Zr₈Ni₂₁, which is stable at least down to 800 °C. ZrNi₃ is formed in a reaction between Zr₈Ni₂₁ and Zr₂Ni₇ at 920 ± 10 °C. Crystallographic data for the intermediate phases in the HfNi and ZrNi systems in the region 65–75 at.% Ni are presented.     

The crystallographic and magnetic structure of Ni2O3H

A nickel oxide hydroxide, nominally Ni₂O₃H, has been synthesized using hydrothermal techniques. The crystallographic and magnetic structures of the material have been determined at 4.5 K from powder neutron diffraction data. The material, which is nonstoichiometric with respect to Ni and H, contains Ni²⁺ and Ni⁴⁺ rather than Ni³⁺ and is orthorhombic (space group Pnmn; a = 5.084(1) Å, b = 2.9103(6) Å, c = 13.954(3) Å). Magnetic moments are aligned along the c axis with antiferromagnetic order. Powder neutron diffraction data collected above the Néel temperature, at 298 and 473 K, revealed no significant changes to the structure or localized electron model.     

The Ternary System Nickel/Silicon/Titanium Revisited

The constitution of the ternary system Ni/Si/Ti is investigated over the entire composition range using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), differential thermal analysis (DTA), and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases τ₁NiSiTi, τ₂Ni₄Si₇Ti₄, τ₃Ni₄₀Si₃₁Ti₁₃, τ₄Ni₁₇Si₇Ti₆, and τ₅Ni₃SiTi₂ are corroborated. For the remaining phases the compositions are determined as Ni₆Si₄₁Ti₅₃ (τ₆), Ni₁₆Si₄₂Ti₄₂(τ₇), and Ni₁₂Si₄₅Ti₄₃ (τ₈). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of τ₁NiSiTi, the only congruently melting phase.     

La5Al3Ni2 – an Intermetallic Phase Observed upon Crystallization of La50Al25Ni25 Metallic Glass

The yet unknown intermetallic phase La₅Al₃Ni₂ was obtained by partially crystallizing amorphous La₅₀Al₂₅Ni₂₅ at 550 K (further heating above 600 K leads to irreversible disappearance of this phase), and its crystal structure was determined from X‐ray powder diffraction data. The crystal structure of the La₅Al₃Ni₂ phase constitutes a new structure type (Cmcm, a = 14.231Å, b = 6.914Å, c = 10.460Å, oC40) and is built from [Al₃Ni₂] chains surrounded by La atoms. In the ternary system La‐Al‐Ni La₅Al₃Ni₂ is located on the section La₅₀Al_50−nNi_n (0 ≤ n ≤ 50) with the binary compounds LaAl and LaNi as end members. Strikingly, also the crystal structures of the end members can be conceived as chain structures with Al and Ni chains surrounded by La, respectively.     

Synthesis and Physicochemical Properties of a Lanthanum-Containing Analog of the Mineral Berthierite FeSb<Subscript>2</Subscript>S<Subscript>4</Subscript>

Phase equilibria in the FeSb₂S₄–FeLa₂S₄ system were studied by physicochemical analysis methods (differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements), and the phase diagram of the system was constructed. The formation of quaternary sulfide FeLaSbS₄ melting congruently at 1230 K, an analog of the mineral berthierite FeSb₂S₄, was detected. The X-ray powder diffraction analysis showed that FeLaSbS₄ belongs to the berthierite structural type and crystallizes in the orthorhombic system with the unit cell parameters a = 11.424 Å, b = 14.160 Å, c = 3.782 Å, Z = 4, and space group Pbam.     

Phase equilibria at 1375 K in three-component system of nickel-chromium-tantalum

The isothermal section of the phase equilibria diagram of the Ni-Cr-Ta system has been constructed at 1375 K by means of the method of equilibrium alloys and existence of six three-phase equilibria has been established, including γ-Ni + β-Cr + α; β-Cr + α + γ; α + γ + Ni₂Ta; γ + Ni₂Ta + μ; μ + γ + NiTa₂ and γ + NiTa₂ + β-Ta. It is shown that both cubic and hexagonal modifications are indicated in Laves binary phase.     

A high-temperature neutron diffraction study of pure and scandia-stabilized zirconia

A high-temperature neutron diffraction apparatus has been used to study a section of the zirconia-scandia system; the purpose was to determine whether this technique can be generally applied to phase equilibria studies. The structure of the tetragonal form of zirconia at 1200°C has been confirmed, and the parameters obtained were z(4d) = 0.188 ± 0.002, B₀ = 2.50Ų, B_Zr = 0.80 Ų, and R = 0.045. The effect of substituting scandia into the tetragonal zirconia structure was studied and the transformation of the ordered low-temperature β-phase to a grossly nonstoichiometric fluorite phase was also observed.     

Phase equilibria in the Cu<Subscript>2</Subscript>S–La<Subscript>2</Subscript>S<Subscript>3</Subscript>–EuS system

Phase equilibria in the isothermal (970 K) and polythermal LaCuS₂–EuS, Cu₂S–EuLaCuS₃, LaCuS₂–EuLa₂S₄, and EuLaCuS₃–EuLa₂S₄ sections of the Cu₂S–La₂S₃–EuS system have been studied. EuLaCuS₃ (annealing at 1170 K) is of orthorhombic system, space group Pnma, a = 8.1366(1) Å, b = 4.0586(1) Å, c = 15.9822(2) Å, is isostructural to Ba₂MnS₃, and incongruently melts by the reaction EuLaCuS_3cryst (0.50 EuS; 0.50 LaCuS₂) ? 0.22 EuS SS (0.89 EuS; 0.11 LaCuS₂) + 0.78 liq (0.39 EuS; 0.61 LaCuS₂); ΔН = 52 J/g. The Cu₂S–La₂S3–EuS system has been found to contain five major subordinate triangles. At 970 K, tie-lines lie between EuLaCuS₃ and the Cu₂S, EuS, LaCuS₂, and EuLa₂S₄ phases and between the LaCuS₂ phase and the γ-La₂S₃–EuLa2S4 solid solution. Eutectics are formed between LaCuS₂ and EuLaCuS₃ at 26.0 mol % of EuS and T = 1373 K and between EuLaCuS3 and EuLa₂S₄ at 29.0 mol % of EuLa₂S₄ and T = 1533 K.     

Phase Equilibria in Systems DyCuS<Subscript>2</Subscript>–EuS and Cu<Subscript>2</Subscript>S−Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>−EuS

The phase diagram of system DyCuS₂–EuS has been first constructed, and the phase equilibria in the Cu₂S–Dy₂S₃–EuS triangle at 970 K have been studied. Compound EuDyCuS₃ (1DyCuS₂ : 1EuS), space group Pnma, a = 10.1901(3) Å, b = 3.9270(1) Å, c = 12.8468(3) Å, melts incongruently at 1727 ± 7 K according to the reaction: EuDyCuS_3solid ? 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS₂) + 0.83 liq (42 mol % EuS, 58 mol % DyCuS₂), ΔH = 2.9 ± 0.6 kJ/mol; microhardness of the phase is 3080 ± 35 MPa. Compound EuDyCuS₃ is transparent in the range 3000–1800 cm^–1. In system DyCuS₂–EuS, the solid solution (SS) based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS₂, 2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS₂ and EuDyCuS3 at 12 mol % EuS, T = 1487 ± 8 K. In system Cu₂S?Dy₂S₃?EuS, 10 secondary systems have been isolated. At 970 K, tie-lines are located between compound EuDyCuS₃ and solid solutions based on compounds β-Cu₂S, EuS, DyCuS₂, β-(DyCu₃S₃), and EuDy₂S₄; between DyCuS₂ and the solid solution of α-Dy₂S₃, DyCuS₂, and EuDy₂S₄.     

Phase equilibria in the Na,K‖CO3,HCO3,F-H2O system at 50°C

Phase equilibria in the Na,K??CO₃,HCO₃,F-H₂O system at 50°C have been determined using the translation method. The system is found to be characterized by the existence of 21 divariant double-saturation fields, 19 monovariant triple-saturation curves, and six invariant quadruple-saturation points. A looped phase diagram (phase complex) for the title system at 50°C has been constructed.     

The synthesis and structure of potassium cyanotrimethylaluminate

The reaction of KCN with Al(CH₃)₃ to form K[Al(CH₃)₃CN] is greatly facilitated by the presence of an aromatic solvent: for p-xylene a solid complex, K[Al(CH₃)₃CN]·C₆H₄(CH₃)₂, has been isolated. The crystal structure of potassium cyanotrimethylaluminate has been determined from three-dimensional X-ray data measured by counter methods. K[Al(CH₃)₃CN] crystallizes in the monoclinic space group C2/c with cell dimensions a = 19.902(7), b = 9.211(4), c = 9.615(4) Å, β = 107.74(5)°, and p_calcd. = 1.09 g cm^?1 for Z = 8. Least squares refinement gave a conventional weighted R factor of 4.9% for 807 independent reflections. The monomeric [Al(CH₃)₃CN]^? units possess no crystallographic symmetry, and the packing in the unit cell is such that the nitrogen atoms on three such units approach the potassium atom to within 3.11 Å. The average aluminum-methyl carbon bond distance is 1.971 (7) Å, while the aluminum-cyano carbon distance is 2.047 (7) Å. This significant lengthening is attributed to partial electron deficiency in the aluminum-cyano carbon bond.     

The system NiAl2O4Ni2SiO4 at high pressures and temperatures: Spinelloids with spinel-related structures

Phase relations in the system NiAl₂O₄Ni₂SiO₄ were studied in the pressure range 1.5 ～ 13.0 GPa and in the temperature range 800 ～ 1450°C. Two new phases, IV and V, were found in regions of pressure higher than 4 GPa. Phase V disproportionates into a mixture of Ni₂SiO₄-spinel, NiO, and Al₂O₃ at approximately 9.5 GPa and 1100°C. Phases III, IV, and V form a solid solution in some compositional range: phases IV and V have a composition around NiAl₂O₄·Ni₂SiO₄, whereas phase III spreads from NiAl₂O₄·Ni₂SiO₄ to the NiAl₂O₄-rich side. All the phases I ～ V are structurally considered to be spinel derivatives, “spinelloids,” with three kinds of tetrahedral groups; isolated tetrahedra TO₄, linked ones T₂O₇, and triply linked ones T₃O₁₀. The ratios of isolated tetrahedra to linked ones are large in the higher-pressure phases and small in the lower-pressure phases. The difference of compositional range of phase III from that of phases IV and V is possibly explained by the avoidance of linked tetrahedra such as O₃AlOAlO₃.     

Crystal structure and magnetic properties of Ba2Ni3F10

Ba₂Ni₃F₁₀ is monoclinic (space group $\text{C2}\text{m}$), a = 18.542(7) Å, b = 5.958(2) Å, c = 7.821(3) Å, β = 111°92(10). Ba₂Co₃F₁₀ and Ba₂Zn₃F₁₀ are isostructural. The structure has been refined from 995 reflections by full-matrix least-squares refinement to a weighted R value of 0.048 (unweighted R, 0.047). The three-dimensional network can be described either by complex chains connected to each other by octahedra sharing corners or with an 18L dense-packing sequence. The basic unit (Ni₃F₁₀)^4? is discussed and compared to the different unit existing in Cs₄Mg₃F₁₀. Antiferromagnetic properties of Ba₂Ni₃F₁₀ (T_N = 50 K are described.     

Structural aspects of the metal-insulator transition in V4O7

V₄O₇ has a transition with decreasing temperature at 250 K and the structure has been refined at 298 and 200 K. The triclinic structure (A$\text{1}$) consists of rutile-like layers of VO₆ octahedra extending indefinitely in the a-b plane and four octahedra thick along the c-axis. The average VO distances for the four independent V atoms are 1.967, 1.980, 1.969, and 1.984 Å at 298K and 1.948, 1.992. 1.961, and 2.009 Å at 200K. At 200K there is a clear separation into strings of V³⁺ or V⁴⁺ ions running parallel to the pseudorutile c-axis. In addition, all of the 3+ and half of the 4+ sites are paired to form short VV bonds. The remaining V⁴⁺ atom is displaced toward one oxygen so as to balance its electrostatic charge. The distortion at the metal-insulator transitions in V₄O₇, Ti₄O₇, VO₂ + Cr, and NbO₂ are compared.     

Clathrate Formation in the Water–Tetraisoamylammonium Propionate System: X-ray Structural Analysis of the Clathrate Hydrate (i-C5H11)4NC2H5CO2·36H2O

In this work X-ray single crystal structural analysis was carried out on the clathrate hydrate of tetraisoamylammonium propionate with the composition (i-C₅H₁₁)₄NC₂H₅CO₂·36H₂O. The hydrate was found to have an orthorhombic structure in space group Cmc2 ₁ with unit cell parameters: a = 21.281(2) Å, b= 12.010(7) Å, c = 24.768(3) Å (150 K). X-ray powder diffraction studies were performed of the hydrate phase, crystallized in the water–(i-C₅H₁₁)₄NC₂H₅CO₂ system in the concentration range of the salt (10–25 wt%) that is the crystallization region of the studied polyhydrate, according to the phase equilibria data. It was found, that in the given concentration region the same hydrate of orthorhombic structure is formed, unit cell parameters, obtained at 20 °C: a = 21.454(13) Å, b = 12.156(4) Å, c = 25.030(14) Å, are in a good agreement with the data of single crystal structural analysis.     

Methane conversion with carbon dioxide on nickel aluminides

The catalytic activity of several samples based on nickel aluminides in methane conversion with carbon dioxide was studied. Nickel aluminides were prepared by the method of self-propagating high-temperature synthesis. The Ni₃Al system containing the nickel metal phase exhibited high activity at temperatures above 1073 K. The systems based on Ni₂Al₃ and NiAl only containing intermetallic compound phases were inactive.     

Phase relations and crystal structure of τ6-Ti2(Ti(0.16)Ni(0.43)Al(0.41))3

Ti(2)(Ti(0.16)Ni(0.43)Al(0.41))(3) is a novel compound (labeled as τ(6)) in the Ti-rich region of the Ti-Ni-Al system in a limited temperature range 870 < T < 980 °C. The structure of τ(6)-Ti(2)(Ti,Ni,Al)(3) was solved from a combined analysis of X-ray single crystal and neutron powder diffracton data (space group C2/m, a = 1.85383(7) nm, b = 0.49970(2) nm, c = 0.81511(3) nm, and β = 99.597(3)°). τ(6)-Ti(2)(Ti,Ni,Al)(3) as a variant of the V(2)(Co(0.57)Si(0.43))(3)-type is a combination of slabs of the MgZn(2)-Laves type and slabs of the Zr(4)Al(3)-type forming a tetrahedrally close-packed Frank-Kasper structure with pentagon-triangle main layers. Titanium atoms occupy the vanadium sites, but Ti/Ni/Al atoms randomly share the (Co/Si) sites of V(2)(Co(0.57)Si(0.43))(3). Although τ(6) shows a random replacement on 6 of the 11 atom sites, it has no significant homogeneity range (~1 at. %). The composition of τ(6) changes slightly with temperature. DSC/DTA runs (1 K/min) were not sufficient to define proper reaction temperatures due to slow reaction kinetics. Therefore, phase equilibria related to τ(6) were derived from X-ray powder diffraction in combination with EPMA on alloys, which were annealed at carefully set temperatures and quenched. τ(6) forms from a peritectoid reaction η-(Ti,Al)(2)Ni + τ(3) + α(2) ? τ(6) at 980 °C and decomposes in a eutectoid reaction τ(6) ? η + τ(4) + α(2) at 870 °C. Both reactions involve the η-(Ti,Al)(2)Ni phase, for which the atom distribution was derived from X-ray single crystal intensity data, revealing Ti/Al randomly sharing the 48f- and 16c-positions in space group Fd3?m (Ti(2)Ni-type, a = 1.12543(3) nm). There was no residual electron density at the octahedral centers of the crystal structure ruling out impurity stabilization. Phase equilibria involving the τ(6) phase have been established for various temperatures (T = 865, 900, 925, 950, 975 °C, and subsolidus). The reaction isotherms concerning the τ(6) phase have been established and are summarized in a Schultz-Scheil diagram.     

New Heptafluorozirconates and ‐hafnates AIBIIZr(Hf)F7 (AI = Rb,Tl; BII = Ca,Cd) – Synthesis,Structures, and Structural Relationships

Four new ABZrF₇ heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (n^o63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF₂ or CdF₂ and ZrF₄ (HfF₄) in sealed platinum tubes at temperature ranging from 550 °C (Tl) to 600 °C (Rb). The crystal structures of both RbCdZrF₇ and TlCdZrF₇ have been solved from single‐crystal X‐rays diffraction data. Rietveld refinements were performed from X‐rays powder patterns for RbCaZrF₇ and TlCaZrF₇. In this series of heptafluorides, both B²⁺ and Zr⁴⁺ cations exhibit a pentagonal bipyramidal 7‐coordination. Their structural relationships with other heptafluorozirconates A^IB^IIZrF₇ as well as β‐KYb₂F₇ are discussed. RbCaZrF₇: a = 6.863(1) Å, b = 11.130(1) Å, c = 8.485(1) Å; TlCaZrF₇: a = 6.868(1) Å, b = 11.165(1) Å, c = 8.486(1) Å; RbCdZrF₇: a = 6.780(1) Å, b = 11.054(4) Å, c = 8.420(4) Å; TlCdZrF₇: a = 6.784(3) Å, b = 11.099(2) Å, c = 8.424(9) Å.     

The interaction of aromatic hydrocarbons with organometallic compounds of the main group elements. : IV. The preparation and structure of the novel selenide K[CH3Se{Al(CH3)3}3] · 2C6H6

The crystal structure of K[CH₃Se {Al(CH₃)₃}₃] · 2C₆H₆ has been determined from single-crystal X-ray diffraction data collected by counter methods. The compound crystallizes in the triclinic space group P$\text{1}$ with cell dimensions a = 17.165(7), b = 10.144(7), c = 10.156(7)Å, α = 119.26(5), β = 104.07(5), ψ = 80.51(5)°, and Dc = 1.12 gcm^?3 for Z = 2. Least-squares refinement gave a final R value of 0.083 for 1967 independent observed reflections. One of the two benzene molecules in the asymmetric unit has been located by difference Fourier techniques. Because of either extreme disorder or high thermal motion, the aromatics make practically no contribution to the X-ray scattering. The selenium atom in the anion exhibits tetrahedral coordination. The Al-Se bond lengths average 2.578(5)Å, and the Se-C distance is 1.93(2)Å.